Abstract : Two groups of young volunteers, one from a sea level area and the other from an elevation of 1610 meters were studied at an elevation of 3475 meters for periods of 24 and 20 days, respectively. The data suggest that after the first week of exposure, there is no increase or decrease in the energy requirements of men living at altitudes of 3475 meters and performing moderate physical activities. The question as to the best nutrient composition of the diet at this altitude was investigated, and it is suggested that the composition and distribution of the food calories consumed are a matter of food habit and preparation. Preliminary information on blood changes reveals that there may be some voluntary dehydration during the first week of high altitude exposure. Information was evaluated on the individual food preferences and acceptability of the US Army ration used in this study. (Author)